As noted in the first answer above, the surface to be tiled, in your case the floor, must be flat within 1/8” in 10' when measured from the high points of the floor. To achieve this, be sure to use the appropriate patch or self-leveling compound (with the same manufacturer's primer), but never thin set mortar.
If your subfloor is not level, it can lead to misaligned tiles and flaking grout during installation. This is not ideal for any homeowner who wants a perfectly tiled floor. Therefore, levelling your concrete floor is a key step before starting any tiling project.
Crooked tiles can occur for a number of reasons. The grout may have been spread unevenly, or the contractor may have neglected to use spacers or battens (small rods) to hold the tiles in place as the grout cured. Wall tiles that sag in certain areas may lack sufficient support.
As tiles have become larger in size, it's become even more important to ensure that the substrate below is perfectly flat and level. An uneven subfloor gives less margin for error as porcelain tiles are rigid and can't cover over any imperfections.
There are flatness requirements for both floors and walls. The TCNA Handbook states that for tiles with all edges shorter than 15”, maximum allowable variation is 1/4” in 10' from the required plane, with no more than 1/16” variation in 12” when measured from the high points in the surface.
Loose and uneven flooring are among the problems that lead to the National Floor Safety Institute calling “hazardous floors” the leading cause of more than 1 million emergency room visits for slip-and-fall injuries each year.
The Australian Standard AS 3958.1 (Guide to the installation of Ceramic Tiles) states a maximum 2mm lippage between standard tiles. A perception of lippage may not necessarily be due to poor workmanship.
Tile Conditions
If they are loose or cracked, it's inadvisable. For existing tiles that are unlevel or for tiles that are protruding, you can also apply a leveling compound across the entire span of tile to even it out properly before putting down laminate.
When renovating your floors, you won't necessarily have the perfect blank canvas. In terms of tiling, an uneven surface can throw up all sorts of problems, distorting the beauty and regimented feel of a flooring project.
To determine whether the existing tile is in good condition and can accept another tile on top of it, use a tool to gently hit the tile. A hollow sound indicates that the tile is not adhered properly. If this is the case, then the whole floor should sound hollow because of the uniformity of the substrate.
14-3 “Horizontal Surfaces/General Notes,” Section 4.0−Lippage) simply says lippage should be limited to 1 mm (1⁄32 in.)
Uneven or sloping floors are very common in older homes, and while it's often a sign of structural damage, it doesn't have to be a dealbreaker.
There are a number of possible solutions for tiling an uneven floor depending on the condition of the substrate. Deep holes must be filled first with a repair mortar. A levelling compound will give a smooth surface, but this does not help with uncalibrated stone where a thick bed adhesive must be used.
Lippage is a situation referring to the difference in elevation between two adjacent tiles that are installed on the floor or wall¹. The larger the size of the tiles (length is more than 450mm), the higher possibility that they are not completely flat.
The best flooring for uneven floors due to its attractiveness and durability is epoxy, which can also be designed to mimic a wide variety of appearances. Not only will epoxy finish out the floor, but it'll also even it out.
Again, the wider the grout joint, the more one can minimize tile irregularities and minimize lippage. On the other hand, the more narrow the grout joint, the less one can compensate for irregularities within the tile or its substrate.
If you're tiling a really uneven surface, sometimes the best solution is to opt for mosaic tiling. This involves using much smaller pieces of tiles of various shapes to create a well-covered wall that minimises the effects of an uneven surface.
Without proper subfloor preparation, your tiles can crack. This can happen because the subfloors are either left uneven or dirt and large debris still cover its surface as the tile is laid.
There are standards that exist within Australia regarding levelling floors. These standards require that there must be 10mm maximum tolerance within any room and 20mm maximum tolerance over the entire building footprint.
So in general, most tiles won't have more than about 1/32" of warpage; thus the maximum allowable lippage is generally at about 1/16" for most quality ceramic tiles.
The tolerance to European standards on this finish of tiles is up to 3mm. They don't normally vary this much but these are the tolerances that are deemed acceptable. It follows that a joint width of 3-5mm is recommended for natural edged porcelain tiles. Porcelain tiles can also come with a 'rectified' edge.
Whether you're a homeowner or looking to buy a home, you should never ignore uneven floors. Sagging, sloping, and buckling floors is a sign of a much bigger problem that can cause serious issues in the future. Fixing the problem sooner will save you money and prevent your home from experiencing further damage.
A staggered or off-set pattern is the most common way of laying tile. There is nothing wrong with sticking with a classic! But if you want to make the look unique, consider dramatic grouting or square tile. Tile can be staggered on the center (or half) of each tile or on the third.